1. Field of the Invention
The present invention generally relates to ultrasonic inspection devices and in particular to inspection devices which are placed in direct contact with the work under inspection.
2. General Background
Ultrasonic examination of work such as pressurized water reactor vessels is typically performed from the inside of the vessel. During such examinations, ultrasonic transducers are manipulated by a remotely operated apparatus to scan predetermined areas of the reactor vessel. The examination is accomplished by generating an ultrasonic sound wave which is acoustically coupled to the vessel being inspected. The sound wave travels through the material of the vessel at a rate determined by the acoustic velocity of the material.
The acoustic velocity is a product of the material's density and elasticity. Reflections or echos of the sound wave occur whenever the velocity of the propagated sound wave is altered. The magnitude of the echo is related to the acoustic impedance of the reflecting material interface or, in the case of a flow, its size and orientation in relation to the size and orientation of the transmitted sound wave. Two methods of coupling the transmitted sound wave from the transducer to the vessel under inspection are generally used. In one, known as the immersion method, the transducer is submersed in water and placed a set distance, generally several inches, from the vessel wall. The sound waves are transmitted from the transducer, through the water, and into the vessel wall. Reflected sound waves are received by the transducer and electronically processed to determine the location of the reflection. A second method of inspection, the contact method, places the ultrasonic transducers in direct contact with the vessel under inspection. The sound is coupled to the vessel by a thin film of water. The transducer may be attached to a remotely operated manipulating system such as an automated reactor inspection system (ARIS) which controls the positioning of the transducer head inside the reactor vessel. As far as is known, previous applications of the contact method of inspection have involved the use of rigid plates specifically contoured for each geometric configuration examined in the vessel. A problem with this method is that several different plates would be required for a typical vessel inspection. Normally, the entire inspection tool must be removed from the vessel to change the inspection plate. Removal of the inspection tool to change out the inspection plate is impractical as such examinations are usually critical path. Ultrasound systems of which the inventors are aware include the following.
U.S. Pat. No. 4,489,729 entitled "Ultrasound Imaging System" is aimed at general applicatins for the medical field and discloses the use of a plurality of transducers, range signal means, timing means, energizing means for the transducers, means for listening for an ultrasonic wave, means for selecting a sequence of firing transducers, and means for producing an output representative of the received ultrasound signals.
U.S. Pat. No. 4,210,028 entitled "Method and Apparatus for Ultrasonically Measuring Concentrations of Stress" is aimed at vessel inspections and discloses an ultrasonic transducer array, means for measuring the time of flight of the acoustic waves within the object of interest, and means for determining from the time of flight measurements any variations in the acoustic velocity of the acoustic waves within the object of interest.
U.S. Pat. No. 4,096,755 entitled "Ultrasonic Inspection Apparatus" is aimed at inspection of aircraft fuselage components and discloses a carriage movable over a surface to be ultrasonically inspected, alternate transmitting and receiving ultrasonic transducers mounted on the carriage, means for causing each of the transmitting transducers to generate a burst of sound in the surface, separate detectors for each of the receiving transducers for detecting a shift in phase in the sound received by its associated receiving transducer due to a defect in the surface and for momentarily indicating a shift in phase indicative of a defect, a single master indicator for all transducers, and means for actuating the master indicator.
U.S. Pat. No. 4,252,022 entitled "Detection, Characterization and Studying of Flaws in Work by Acoustic Imaging" relates to acoustical holography and discloses a method of studying flaws in work having an irregular surface comprising generating and focusing acoustic energy on or near the irregular surface, scanning the surface with the focused acoustic energy, receiving resulting acoustic energy from echoes from flaws, and controlling the reception to reduce the effects of differences in the irregular surface.
U.S. Pat. No. 4,523,468 entitled "Phased Array Inspection of Cylindrical Objects" is aimed at pipe inspection and discloses a method of ultrasonically locating defects in an object with first and second transducer arrays comprising actuating at least one transducer of each array and causing the remaining transducers to assume a reflected receiving mode, measuring an ultrasonic wave travel time between transmission and receipt, determining the spatial relationship between the transmitting and receiving transducer, and determining the location of the defect from the measured travel time and relative spatial relationship of the transducers.
U.S. Pat. No. 4,604,897 entitled "Multitransducer Ultrasonic Transducer With Transducers of Different Sizes" discloses the use of probes of different sizes and control means for selectively activating successive groups of transducers.
U.S. Pat. No. 4,582,065 entitled "Ultrasonic Step Scanning Utilizing Unequally Spaced Curvilinear Transducer Array" discloses an assembly for use in a medical diagnostic system comprising a plurality of individual ultrasonic transducer elements and a mounting structure defining a curved array face for disposing the transducer elements in a convex curvilinear array.
The known art does not address the problem of variations in the water path distance in immersion testing. The use of several contact heads shaped to match the contour of the portion of the vessel under examination, a time consuming and impractical process, is also not addressed in the area of contact testing.